electrical ground/neutral question

[Mikepier]

I know this has probabaly been discussed before, but I wanted some opinions for a problem I discovered. The other day, I go to open my garage door barefoot and I got a slight electrical shock from the handle. I checked the voltage from the door handle to ground and found 20 VAC. What I discovered is that the outlets in my garage are not grounded, and since one of the walls in my garage is metal studs, I guess the stray voltage made its way from the metal studs to the garage guide rails and to the door. I put a test light from the studs to ground, but the light did not work and the residual voltage dropped to 0. I just had a new panel installed last year with some GFCI breakers since some of my wiring has no ground. I thought the GFCI breaker would trip in this situation, but it did not. Basically I guess the right thing to do is run a ground wire, or new grounded circuit to the garage. Unfortunately its a pain to do this. Since the neutral and ground are tied together in the panel, isn't it the same electricallly if I tied one of the neutrals in the outlet to the metal stud in my garage, which would ground it? Also why didn't the GFI breaker trip when I got shocked?

[Mikepier]

On this particular circuit which has ungrounded romex, I have a GFI breaker for the outlets in the garage.

[Mikepier]

No garage opener.

[RBM]

Do you have a garage door operator and a metal garage door? Is the outlet that the door opener is plugged into on the gfci circuit?

[Mikepier]

This is an attached garage. But can I just run a piece of #12 green to a nearby outlet in my den that I know is grounded, instead of running it to the panel? (which is on the opposite side of my house in the basement.)

[zxcvbob]

Is this an attached garage? Run a ground wire to it from the main panel. You cannot use the neutral as a ground because they are not the same thing -- except at the one point where they are connected back at the main panel. You shouldn't have to run all new grounded cable, just a #12 green wire. It's usually not all that hard to do.

If it's a detached garage, you need to install a grounding electrode (ground rod) or two, and you can connect the grounds and neutrals (and the metal building) together at the point where you connect the grounding electrode -- it should be the first box where the circuit comes in.

This is an oversimplified description and therefore probably not 100% accurate, but I hope it helps.

Bob

[zxcvbob]

You could in 1993 (that's how old my code book is) as long as you were just updating an existing ungrounded circuit.

Whether or not it's still legal, it's a lot safer than what you have now.

Bob

[Joseph Meehan]

I suspect that you are getting induced current. That happens when there is no direct connection. A small amount of current flows as in a transformer across an opening without any direct connection. This only happens with AC current and in general even a high resistance (light bulb) will drain it off quickly.

The GFI did not trip because the current because it was not a direct connection.

I do suggest that you prooerly ground your outlets in the garage. Are all your garage circuits GFI protected?

[EXT]

In addition to grounding your electrical outlet the metal frame (studs) of the garage should also be grounded to prevent them from becoming accidentally electrified or even the problem that you have. I don't know if it is code to ground metal stud walls but in structural steel buildings the steel frame must be grounded. However if you install a grounded line with metal boxes, the electrical ground will be connected to the steel studs through the steel box.

[Chris Lewis]

According to Mikepier :

Do you get 20VAC from the wall studs to ground too?

No, NEVER attach use the neutral as a ground. If it ever becomes detached, the whole garage goes live.

The fact that the residual voltage drops to zero when you put a low impedance device (the test light), means that the current available is very low.

If the GFCI's don't trip when you run a wire from the stud to ground, it's most likely _not_ an electrical leak, and is instead static or induced voltages in the frame of the garage.

According to electrical code, major metal "systems" in buildings need to be grounded - ie: metal studs. You don't have a ground. If a ground is too difficult to install, you might want to consider simply driving in a ground rod and grounding the building frame to it. While this is normally somewhat of a no-no (multiple unconnected grounding/single panel), the GFCIs _will_ detect hot-frame shorts and trip - without GFCI, you'd need to push >>15A thru the dirt to trip - that won't happen. The GFCI's work on just a few ma and won't have a problem.

[HorneTD]

NO, You can run the separate green wire but it must run to the panel or to some point on the grounding electrode system!

[John Gilmer]

Well, some things are beyond the scope of the NEC.

It's entirely up to him whether he decides to make an effort to "ground" most of the exposed metal in his garage or just let it "float."

Were I getting shocks, I damn well would certainly starting grounding stuff. I would also start looking very hard for the leakage paths. I might replace the outlet where a powered door opener in plugged in to a GFCI type. Unfortunately, many "electronic" packages such as a radio receiver have a network that connects HOT and NEUTRAL and GROUND (frame/chassis) together. The leakage from this network is supposed to be well below the threshold to trip a GFCI but ...

Certainly, he should "ground" metal that gives him a shock.

[maradcliff]

There is a very unusual thing that happens if a GFI gets defective. I know because I had it happen. I had a GFI on the side of the house and am on a farm. I put some horses on the rear lawn to mow the lawn, when the weather suddenly turned to cold (November). Their water trough froze up, so I put a tank heater into the tank and plugged it into an extension cord and into the GFI. What I did not know was the GFI was defective. For some reason the 3rd prong (ground) on the face of the GFI was not connected to the circuit. The extension cord apparently picked up a capacitance putting a slight tickle of electricity into the water. The horses would not drink out of the plastic tank. They kept kicking it and making a fuss everytime they went to it. I finally decided to test it. First I touched the water and felt nothing (rubber boots). Then I touched the ground with my other hand and got a tickle. My meter showed around 15 volts to ground. With my meter I eliminated the extension cord as being defective and discovered the GFI had no ground coming out, even though it was well grounded in the box. I replaced the GFI and the electrical leak was gone. However, the horses continued to fear the water. One of them got sick from lack of water and cost me $400 in vet bills and he almost died, but survived. I had to spend another $70 on a new water trough that looked different, and move it to another place in the yard. (Horses remember things like that, but when things change then they are ok again).

So, $500 later and several sleepless nights everything was back to normal. All because of a faulty GFI.

Mark

On 4 Aug 2005 02:00:54 -0700, "Mikepier" wrote:

[John Gilmer]

IF the GFCI "passes" the push button self test, then it would still provide protection even if the ground lead was not connected. With the ground, it might have tripped just from the bad cord, of course, and your animals would be somewhat better adjusted now.

Sorry about your experience. You may want to invest in a combination outlet tester/GFCI tester. (It plugs into the outlet: two of three neon lamps should light. It has a test button which should TRIP the GFCI protected circuit. They sell for less than $20 (and cost about $1 to make.)

[maradcliff]

Thanks. I bought one of those GFI testers after that, and regularly test all of the GFIs used near the animals. I almost had a horse electricuted from a shorted tank heater years ago. So I installed GFIs for every heater and any possible place I might use one of those heaters. I thought I was safe after that. What happened to that GFI was a very rare and weird thing. I even had the electric company puzzled when I called them before I did any testing, because I assumed the farm had a bad ground (called stray voltage on farms). They came out, tested the electrical system, and could not explain the problem. I never expected a bad GFI and to this day I still can not totally understand what happened internally to cause that. If I recall correctly, the button did trip, but no ground coming out. I'm just glad that no animals died. I should note that when I was younger I worked as an electrician for several years, and this really had me puzzled since I had never heard of such a thing happening.

I'd like to hear from anyone else that had this happen, but somehow I have a feeling no one else on here has had this problem. I spoke with another electrician after it happened and they said they never seen it either.

Mark